Symmetrical quaternary ammonium compounds and their use in heavy metals recovery

ABSTRACT

Symmetrical quaternary ammonium compounds of the formula ##STR1## are disclosed, wherein each Ar is identical and is phenyl or a condensed polynuclear aryl group having 2 to 4 aryl nuclei, each R is identical and is alkyl of 1 to 4 carbon atoms, X.sup.⊖ is a salt-forming anion of valence 1 or 2 and n is 1 or 2 depending on the choice of X. Also disclosed are apparatus and processes for the recovery of heavy metals such as silver, gold and other precious metals from solution in water. The disclosed quaternary ammonium compounds are adsorbed to a suitable substrate, preferably alumina, and the treatment water is passed therethrough. A second bed of divided metal such as aluminum is disclosed for use in series with the bed incorporating the quaternary ammonium compounds.

This is a division, of application Ser. No. 113,279 filed Jan. 18, 1980.

FIELD OF THE INVENTION

My invention pertains generally to compounds, and apparatus andprocesses using them, which find particular use in the recovery of heavymetals from waste water and incidental use in the oxidation of toxicanions to less toxic biodegradable anions that may be discharged intoeffluent waters.

BACKGROUND OF THE INVENTION

Recently the interest in reducing the discharge of heavy metals intoenvironmental waters has been spurred by rapidly rising prices for heavymetals, in particular gold and silver. Most industries that use largequantities of heavy metals, such as silver in the photographic industry,recycle used materials and attempt to recover as much metal as possiblefrom waste waters generated during processes using those metals, such asphotographic development.

Previous processes for the recovery of silver from exposed photographicfilm and from waste water from photographic development have sufferedfrom limited silver extraction efficiency and from their inability tocope with the large amounts of toxic thiosulfate anions ormetal-complexed cations that are by-products of photographicdevelopment. My invention is directed to the solution of both of theseproblems.

SUMMARY OF THE INVENTION

I have invented a new class of quaternary ammonium compounds of theformula ##STR2## wherein each Ar is identical and is phenyl or acondensed polynuclear aryl group having 2 to 4 aryl nuclei, each R isidentical and is alkyl of 1 to 4 carbon atoms, X.sup.⊖ is a salt-forminganion of valence 1 or 2 and n is 1 or 2 depending on the choice of X.While Ar is preferably naphthyl or phenanthryl, of any isomericconfiguration, Ar may also be phenyl or other condensed polynuclear Argroups such as anthracene, naphthacene, chrysene, pyrene andtriphenylene. Larger Ar nuclei are difficult to handle in theFriedel-Crafts reactions employed to make these compounds and producecompounds with limited stability.

Each R is identical and is preferably ethyl or butyl. It is necessary, Ihave found, that at least one aliphatic carbon atom separate eachpolynuclear Ar group from the central nitrogen atom of the ammonium ion.X may be any chemically stable salt-forming anion, but it is preferablyhalogen, in particular chlorine. The sulfate ion is also acceptable.

My invention also comprehends apparatus for removing heavy metals fromsolution in water and processes for using the compounds and apparatus Ihave invented in the recovery of heavy metals in aqueous solution. Theheavy metals include but are not limited to silver, gold, the members ofthe platinum family, cadmium, zinc, lead, palladium, rhodium and othertransition metals. Iron is the least electronegative metal which may berecovered from solution using my invention.

The apparatus according to my invention may include a single bed or twobeds connected in series. The first bed through which metal-containingwater is passed comprises a suitable adsorbing substrate and aneffective amount of a quaternary ammonium compound of the formula##STR3## wherein each Ar is identical and is phenyl or a condensedpolynuclear radical having 2 to 4 aryl nuclei, each R is identical andis alkyl of 1 to 4 carbon atoms and X is halogen, deposited on saidsubstrate. Any of the compounds described above may be deposited on thesubstrate in the first bed, but I have found that as the number of Arnuclei rises in the quaternary ammonium compound, the substrate adsorbsthose molecules in preference to molecules having less bulky groups. Thesubstrate may be any suitable material that will adsorb the quaternaryammonium compounds according to my invention, and may be constructed ofsuch materials as silica, thallium oxide, magnesium silicate,diatomaceous earth and activated charcoal, but I have found that thepreferable substrate consists essentially of a suitable aluminum oxide.This aluminum oxide, which in commercial form is sold as "alumina," maynot be in the α-form, since without OH groups in the crystallinelattice, the aluminum oxide will not provide a substrate to whichquaternary ammonium compounds according to my invention will adsorb.Gamma-alumina is preferred.

In the form of my invention in which the apparatus comprises two beds,the second bed consists essentially of a suitably reactive metalselected from Family IA, IIA, IIIB of the Periodic Table in suitablydivided form. Of course, many of the elements in those families, such ascesium, are obviously not suited to the recover of metals from water,but they are theoretically suitable if the heavy metals are in solventswith which the most active members of these families will not react. Themetal in the second bed is preferably either aluminum or magnesium, mostpreferably aluminum, at least about 99% pure, in particle sizes rangingfrom about 30 to about 50 mesh and substantially free of surface oxides.This second bed may or may not, as is dictated by the needs of theinstallation, be used in conjunction with the more preferred embodimentsof the first bed.

In addition to providing a new family of compounds, my invention has thefeature of improving the quality of waste waters produced by processesusing heavy metals, in particular photographic development processes, bythe stabilization of heavy metal anions, most particularly thiosulfatecomplex anions. The heavy metals are removed from the soluble state assulfides or other such insoluble compounds and are trapped in the filterbeds.

The first bed provides the unique feature that it is self-regenerating,requiring no backwashing or regenerative chemicals.

A further object of this invention is to provide a process for theremoval of heavy metals from solution which is both efficient and whichcan be practised over long periods of time as compared with the priorart processes without the need for repair or replacement of filterelements. When the filter of the first bed is used to extract silver andsuch similar metals from thiosulfate waste waters produced byphotographic processes, it has an active life range of from 30 to asmuch as 150 days, depending upon the flow rate and concentration ofheavy metals.

It is yet a further feature of the invention to provide efficient newion exchange agents for the recovery of heavy metals generally and toprovide apparatus making use of these new agents.

Another feature of the invention is the provision of a second bed whichimproves effluent water quality by oxidizing toxic anions to less toxicbiodegradable anions, while providing additional heavy metal separationwhen used in conjunction with the first bed.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Before setting forth detailed instructions for practicing my invention,I will describe what I understand to be the theory by which my inventionoperates. I do not intend, however, to be bound by this description.

In the first bed, the anion exchange step may be represented as follows:##STR4## "QAS" represents quaternary ammonium salt and "M" represents aheavy metal, such as silver. While the QAS as it is adsorbed to thesubstrate is preferably in the form of a halide, the halide form isconverted to the sulfide form above by the soluble sulfides in the waterto be treated, as the sulfide form is strongly basic. It is ordinarilythought that the thiosulfate ion exists in free form in photographicdevelopment effluent waters, but I have found that the heavy metals arebound to the thiosulfate as a univalent anionic complex. The heavymetals precipitate as sulfides, falling to the bottom of the bed to berecovered later.

The QAS ion exchange agents I have invented display a unique in situregeneration: ##STR5## The adsorbing substrate provides sites for theoxidation of the QAS-thiosulfate form by oxygen dissolved in thetreatment water. This regeneration takes place simultaneously with theanion exchange step depicted above and results in extended first bedlife, of 30 to as much as 150 days, depending on flow rate and heavymetals concentration. This step also oxidizes thiosulfate anion, whichdegrades biologically to noxious hydrogen sulfide, to the sulfate anion,which is non-toxic and is stable towards biodegradation to hydrogensulfide.

In the second bed, the heavy metal-thiosulfate complex not converted inthe first bed is converted to the sulfide by the oxidation of thedivided metal in the bed:

    2A°+2Na[MS.sub.2 O.sub.3 ]+O.sub.2 →Al.sub.2 O.sub.3 +M.sub.2 S↓+Na.sub.2 SO.sub.3 +SO.sub.2

The following is a description of the synthesis of compounds within thescope of my invention. It is understood that phenanthrene and highercondensed aryl compounds may be used in place of naphthalene.

Preparation of tetra [naphthyl-ethyl] ammonium chloride ##STR6##

0.1 mole of anhydrous FeCl₃ and 0.1 mole of naphthalene, dissolved in300 ml nitrobenzene, are introduced into a 3-neck 500 ml flask fittedwith a gas dispersion tube, stirrer and thermometer and placed on an icebath. The stopcock is opened and 0.009 moles (1.9 l at 1.1 atm) ethyleneoxide are introduced into the flask with slow stirring. The reactiontemperature should not exceed 30° C. as the exothermic reactionproceeds.

After 10-15 minutes a straw-colored oily suspension is obtained. At thispoint the flask is removed from the ice bath and 50 ml of 1.0 M aqueousHCl is added. The mixture is gently warmed to 100° C. to drive off theHCl and then is mixed with 300 ml water in a 1000 ml separatory funnel.The funnel bottoms are drawn off and allowed to stand over ice for 24hours, as long whitish needles appear. This mixture is then filtered,the filter cake is washed with CHCl₃ and evaporated to dryness.

The dry crystals are added to 0.10 moles AcOCl, heated gently to driveoff the HCl formed and dissolved in benzene. This solution is passedthrough a 15 mm. O.D.×30.5 cm column packed with MallinckrodtAluminar®C-110 100-200 mesh. The esters are retained in the column whenthe residual unreacted naphthalene is eluted with benzene. The column isthen washed with 25.0 ml 1.0 M NaOH, followed by two water washes. Amixture of 2-(α)-naphthyl ethanol and 2-(β)-naphthyl ethanol is elutedfrom the column with 100 ml hot xylene and recrystallized therefrom. Noattempt was made to separate the isomers. The crystals produced weighed11.34 g, yield 88% of theory, and melted in the range 64°-68° C.##STR7##

10 grams of 2-naphthyl ethanol I are dissolved in 200 ml benzene andtransferred to a 3-neck 1000 ml boiling flask fitted with a 25 mldropping funnel, reflux condenser and thermometer. As the flask isgently agitated on a magnetic stirrer/hotplate, the dropping funnelstopcock is opened and 5 ml SOCl₂ is added dropwise to the solution. Themixture is then refluxed for 2 hours.

After the mixture cools, 50 ml of 1.0 M aqueous NaOH are added. Themixture is shaken well, the bottoms discarded and the mixture is boileddown in a beaker to a volume of 50 ml. The reduced mixture is cooledover ice until the formation of white needles, which are washed withCHCl₃ and recrystallized. When the crystals are redissolved in 25 mlAcOCl, no apparent reaction occurs. To this mixture is added 25 ml of0.1 M NaOH. The product is washed with 50 ml water and filtered, thefilter cake is washed with CHCl₃ and recrystallized. The yield is 10.94g (99% of theory) of crystals of 2-naphthyl ethyl chloride, meltingpoint 56°-58° C. ##STR8##

Dissolve 8 grams (0.042 moles) of III in 100 ml benzene in a 500 mlsingle neck boiling flask fitted with a gas dispersion tube. The flaskis placed in an ice bath atop a magnetic stirrer and SLOW agitationstarted. Through the stopcock on the gas tube are introduced 0.01 moles(0.211 l at 1.1 atm) anhydrous ammonia. The ammonium salt immediatelyforms with the evolution of HCl gas. The flask is then removed from theice bath and 100 ml of 0.01 M NaOH are added. The mixture is shaken welland heated gently to dissolve all of the salt. The mixture is filteredand cooled over ice; 5.9 grams of large white crystals are formed.

The same techniques, which are known to persons experienced in theFriedel-Crafts reaction, suffice to synthesize the other quaternaryammonium compounds which I have invented. The forms in which R is butyl,for example, can be made by using tetrahydrofuran instead of ethyleneoxide. Those seeking further guidance should refer to G. Olah,Friedel-Crafts Chemistry (John Wiley & Sons, New York 1973). The amountsof α- and β-isomer formed depend on the solvent used for the initialreaction; nitrobenzene as the solvent yields 62% β-naphthyl isomer, butI have found that the compounds seem to work equally well regardless ofwhat isomer is used. The choice of which Ar to use depends on theeconomics of the trade-off between the cost of materials and metalrecovery efficiency. The cost of the aryl starting materials risessharply as the number of condensed nuclei increases, but this is offsetby the enhanced adsorption of the bulkier groups to the substrate. Forthe purposes of silver recovery I have found tetra [phenanthrene-ethyl]ammonium chloride to be preferable so far.

The application of the ammonium salt to the substrate involves a firststep of dissolving whatever salt is to be employed in a mixture ofbenzyl and isopropyl alcohols, about 70% benzyl and 30% isopropyl beingpreferred, at about 115° C. Sufficient salt is added to make up asaturated solution, which is then poured thru a canister of conventionaldesign packed with a catalytic grade of commercially available γ-aluminain 100-200 mesh particle sizes. Aluminas as fine as 325 mesh may beused, but they create such a pressure drop across the bed that they arenot suitable for gravity flow operation, requiring instead a pump on thefilter effluent line to ensure continuous flow of the water to betreated. If saturated salt solutions are used, up to 20 grams ofammonium salt can be loaded for each gram of alumina substrate material.In making up the first bed it is advantageous to achieve the heaviestsalt loadings possible. I have found that virtually all of the dissolvedsalt will adsorb to the substrate on the first pass, with the alcoholsolvent mixture running out of the bottom of the bed. After the alcoholhas run out of the bed, the remaining solvent is removed by evaporationto dryness under a vacuum of 5 mm. Hg.

The second bed which is used in the process and apparatus I haveinvented in its more commercially suitable embodiments is simply acanister filled with granules of substantially pure aluminum ormagnesium, aluminum being preferred for its lower cost and because itgenerates far less heat than magnesium. The aluminum may be commerciallyavailable at least 99% pure granules in particle sizes of about 30-50mesh, substantially free of surface oxides.

In the preferred mode of operation the canisters of the first and secondbeds are vertically arrayed to provide gravity flow of treatment waterfrom the input, through the first and second beds, and out the filtereffluent line. The most preferred apparatus comprises the first upperbed and second lower bed separated by a multiply perforated bulkhead,with both beds placed in a single canister. The choice of single or dualcanisters depends on commercial considerations and does not affect theoperation of the apparatus.

The recovery of heavy metals from the beds follows conventionaltechniques. When the first bed becomes depleted (or earlier if desired),the bed material is removed from the canister, water is added ifnecessary and the material is centrifuged. The heavy metal sulfideseparates out as a layer, which is removed and dried under heat until itis "bone-dry." The dried sulfide is thrown directly into a furnace andsmelted for its heavy metals content. The second bed is handled in muchthe same way, except that the greatest portion of the divided metalsubstrate will be spent by conversion to its corresponding oxide.

By the same token the recovery of silver from unneeded photographic filmfollows conventional techniques. The film is first immersed in chloridesolution to convert the silver to the chloride, and then it is washedwith water. The processed film is immersed in a thiosulfate bath whichleaches the silver halide from the film backing. This liquor is thenpassed through the apparatus in accordance with my invention.

This application sets forth preferred embodiments in accordance with therequirements of the Patent Act. It is understood that persons ofordinary skill in this art will make modifications and use equivalentcompounds and apparatus without departing from the scope and spirit ofmy invention as disclosed herein. I intend by the following claims tocover all such modifications and equivalents.

What is claimed is:
 1. A quaternary ammonium compound of the formula##STR9## wherein each Ar is identical and is phenyl or a condensedpolynuclear aryl group having 2 to 4 aryl nuclei, each R is identicaland is alkyl of 1 to 4 carbon atoms, X.sup.⊖ is a salt-forming anion ofvalence 1 or 2 and n is 1 or 2 depending on the choice of X.
 2. Thecompound of claim 1, wherein R is ethyl or butyl.
 3. The compound ofclaim 1 or 2, wherein Ar is naphthyl and R is ethyl.
 4. The compound ofclaim 1 or 2, wherein Ar is phenanthryl and R is ethyl.
 5. The compoundof claim 3, wherein X is halogen and n is
 1. 6. The compound of claim 4,wherein X is halogen and n is
 1. 7. A quaternary ammonium compound ofthe formula ##STR10## wherein each Ar is identical and is a phenyl or acondensed polynuclear aryl group having 2 to 4 aryl nuclei, each R isidentical and is chosen from the group consisting of ethyl, propyl andbutyl, and X.sup.⊖ is a salt forming anion of valence 1 or 2, dependingon the choice of X.
 8. A quaternary ammonium compound as recited inclaim 7 wherein X comprises a halogen.
 9. A qurternary ammonium compoundof the formula ##STR11## wherein each Ar is identical and is chosen fromthe group consisting of phenyl, naphthyl or phenanthryl, each R isidentical and is chosen from the group consisting of ethyl and butyl andX.sup.⊖ is an anion chosen from the group consisting of chloride,bromide, iodide, and sulfate.
 10. A quaternary ammonium compound asrecited in claim 1 or claim 7 wherein X.sup.⊖, the salt forming anion isa sulfate.